Torque from a driving device to a driven device is normally transferred by means of a shaft, being a rotating or stationary component which is normally circular in section. If the shaft is rotating, it is generally transferring power and if the shaft is operating without rotary motion it is simply transmitting torque and is probably resisting the transfer of power, for example an axle of a vehicle. Mechanical components directly mounted on shafts include gears, couplings, pulleys, cams, sprockets, links and flywheels. A shaft is normally supported on bearings. The torque is normally transmitted to the mounted components using pins, splines, keys, clamping bushes, press fits, bonded joints and sometimes welded connections are used. These components can transfer torque to/from the shaft and they also affect the strength of the shaft and must therefore be considered in the design of the shaft.
In the design of a shaft, consideration must be made of the combined effect of all the various forms of loading, such as torque (shear loading), direct shear loading, tensile loading and compressive loading. The design of shafts must include an assessment of increased torque when starting up, inertial loads, fatigue loading and unstable loading when the shaft is rotating at critical speeds. There are many coupling devices in use in research and industry that transfer rotational mechanical power. Known devices comprise a chuck that is adjustable over a relatively wide range. The chuck may be attached to the driver by a threaded or tapered bore or any other suitable means, which will use a grip of the chuck or a key to fasten. However, not only are these mass produced, meaning that they are not balanced as such, they are quite large and are made of steel whereby, in use, provide a substantial amount of inertial resistance, too great for many applications, including metrology, especially in wind direction applications. Additionally, the fastening of a chuck is dependent upon an operator's judgment to apply a correct amount of torque when locking.
FIG. 1 shows a prior art coupling device 1 having a right circular cylindrical chamber with first and a second diameters and a bore, all being concentric with respect to each other, the second diameter being larger than the first diameter. Within the bore, a shaft 2 is a sliding fit, the shaft being operatively positioned therein; the shaft having an annular groove 3 about which, in conjunction with the inside wall of the chamber, about the first diameter, the ball can move, an annular wall of the chamber preventing the relative axial movement of the coupling device with respect to the shaft in one direction; the cap of the coupling device preventing movement in the other axial direction. That is to say, when the ball reaches the position shown in unbroken line in the drawing further outward movement of the shaft is prevented by the locking action of the ball between the sloping side of the groove and the wall and bottom of the chamber. The shaft is then locked in position in the coupling member and cannot be withdrawn while the coupling remains in the vertical position or thereabouts unless vertical acceleration, vibration or magnetic force is used. This pin arrangement has been susceptible to backlash, making the instrument inaccurate.
Release of the coupling element is enabled when the ball is in the position indicated in dashed lines 4′, as shown on the left hand side of the shaft 2 in FIG. 1. Conveniently, downward pressure is exerted on the cap 9—in the direction indicated, against resilient element 5, when the coupling arrangement is inverted, gravity being employed to enable the ball to move. Upon relative movement of the coupling device away from the shaft, the ball is not obstructed by the annular groove and thereby relative movement between the coupling device and the shaft is not impeded and the components can be separated. The axial groove 7 in the shaft and engaging pin 8, passing into the bore of the first member is used to prevent relative angular rotation of the two members of the coupling.
This prior system, however, suffers from a number of issues. One first issue is that the coupling device is not necessarily rotationally located with regard to the shaft unless the pin 8 is employed. Another issue is that the ball 4 is susceptible to being adjacent the axial slot 7 and thereby not guaranteeing continued coupling, noting that the ball is shown 180° to the axial groove: to overcome this issue, an extra ball can be employed, but this could cause difficulties in coupling situations where balance is critical factor.
DE4338278 relates to a device 20 (per FIG. 2) for locking an axially movable securing pin or bolt 22 by the use of a solenoid 22 in a missile environment, where there is an extreme requirement for a high functional reliability. Specifically, this utility model provides a means for locking the axially movable securing pin or bolt by a ball bearing 27 element, which engages in a locking groove 28 on the circumference of the securing bolt by means of a locking ball 27. The solenoid drives a piston 26 via rod 25 within channel 27, the piston being movable so as to enable locking of the shaft 22 by means of the ball bearing. However, this system relates to a remote, electrically controlled arrangement that cannot be utilized in a rotational coupling arrangement.